Monitoring and testing system for a fail operative control system of an aircraft



July 8, 1939 A. T. KIRCHHEIN ETAL 3,454,849 MONITORING AND TESTING SYSTEM FOR A FAIL OPERATIVE CONTROL SYSTEM OF AN AIRCRAFT sheet of Io Filed April l. 1965 1N VENTORS ALBERT 7.' K/RCHHE/N LOU/S J. FRA

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MONITORING AND TESTING SYSTEM FOR A FAIL OPERATIVE CONTROL SYSTEM OF AN AIRCRAFT FIG. 2A ALBERT T. /f/RcHHE/N ou/s J. FRANCH/ ATORNEY July 8, 1969 A. T. KIRCHHEIM ET AL 3,454,849

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MONITORING AND TESTING SYSTEM FOR A FAIL OPERATIVE CONTROL SYSTEM OF AN AIRCRAFT Filed April 1. 1965 sheet 5 of 1o YAW- DAMPER LOGIC NETWORK 455 mi 553A OR GATE SMA l/ 585A 454 I 5356A 550A 452 OR GATE LEVEL IA SENSOR 605A km 930A 59A No.1 P R 300A YAW DAM E a 323A 333A SERVO CLTCH 345A 354A HOA/ CONT l. 340A 337A C NT SOLENOID MF R 335A 375A 39am 092A IB 398A 3u "1F12- 582B jaaa No.2 395A 300B 307 YAW DAMPER sixic 2750s) SOLENOID 275(2B) 3 275(3B) 395B 992A 395B MND PILOTS YYAW OAMPER 4,0 INOPERATIVE 406 LIGHT 2 ||lI-. coPILOrs YAW DAMPER 4|2 INOPERATIVE 43o LIGHT L FAULT LIGHT FAU LT 705 BELAY TIMI CIRCUIT FIG.9

.f MONITOR 27508) TEST LIGHT 275(,2B 275 (3B 395A IN VENTORS B 605A FI G. 4 /IL BERT r /f/RCHHE/N LOU/S J. FRA CH/ July 8, 1969 A T, KlRCI-IHEIN ET AL 3,454,849

MONITORING AND TESTING SYSTEM FOR A FAIL OPERATIVE CONTROL SYSTEM OF AN AIRCRAFT Filed April 1, 1965 sheet 6 of 1o .MODULE FAILURE INDICATOR 00 50| ,03 505 35m 3 *lll 348 fIlllllL I Bf aaovoc 337 323 397 n lm I k i FIG. 6 v33o :373 37| l I 95 CURRENT MONITOR AHORA/5) July 8, 1969 A.T. KIRCHHEIN ET AL 3,454,849

MONITORING AND TESTING SYSTEM FOR A FAIL OPERATIVE CONTROL SYSTEM OF AN AIRCRAFT Filed April 1, 1965 sheer 7 of 1o Yuf Damper P7.' 7'. 5 w/tches 59 pus/z o Tesi /Vewor/Y INVENTUM ALBERT- w/RCHHE/N FIG. 9 OU/5 J. FRA NCH Arron v5/- July 8, 1969 A, T, KlRCHHElN' ET AL 3,454,849

' MONITORING AND TESTING SYSTEM FOR A FAIL OPERATIVE CONTROL SYSTEM OF AN AIRCRAFT Filed April 1, 1965 sheet of 1o FIG-.10

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INVENTORS ALBERT 7.' KlRCHHE/N OU/5 J. FRA CH/ July 8, 1969 A. T. KIRCHHEIN ET AL.

MONITORING AND TESTING SYSTEM FOR A FAIL OPERATIVE ITI-led April I, 1965 CONTROL SYSTEM OF' AN AIRCRAFT lSYSTEM ON-OFF SWITCH 'TEsT' PUSH BUTTON 'TEST' RELAY RATE GYRO SIGNAL FAULT FUNCTION SYSTEM OFF LIGHTS COMPOSITE MONITOR LIGHT CHECK RESET LIGHT FILTER OUTPUT AND SURFACE POSITION -X- Sheet 9 of lO PUSH -TO-TEST SEQUENCE l I I l I 0N I I OFF I I I I I oEPREssED v(SELF-HOLDING) l I l' IDE-ENERGIZED I I I I TOROUEO INORMAL I I I I I I -X- SURFACE POSITION DURING PHASE I ONLY ALBERT /f/RCHHE/N LOU/5 J. FR NCH/ ATTORNEY July 8. 1969 A. T. KIRCHHEIN ET AL 3,454,849 MONITORING AND TESTING SYSTEM FOR A FAIL OPERATIVE f CONTROL SYSTEM OE' AN AIRCRAFT Filed April l, 1965 Sheet United States Patent Office 3,454,849 Patented July 8, 1969 U.S. Cl. S18-18 23 Claims ABSTRACT OF THE DISCLOSURE A monitoring and testing system for a fail operative control system of an aircraft including means for effecting a dynamic phase for testing tracking capabilities of the aircraft control system and a passive phase to detect component failures in the aircraft control system.

This invention relates to improvements in a monitoring and testing system for a fail operative control system of an aircraft and more particularly, the subject matter of the invention relates to the provision of an automatic monitoring system for self-testing of the dynamic command loop and fail operative logic circuitry for a fail operative yaw damper dual control system which may be of a type such as disclosed in U.S\. application Ser. No. 414,564, filed Nov. 30, 1964, by Louis I Franchi, Ralph Sellite and James E. Bulloch, U.S. Patent No. 3,- 379,951, granted Apr. 23, 1968, including a hydraulic power control rudder actuator such as described therein together with a preload override spring device to operably connect each of the dual servo control systems to the hydraulic control, the overload spring device being of a type such as described and claimed in U.S. application Ser. No. 414,086, filed Nov. 27, 1964, by Oscar R. Wermlinger, now US. Patent No. 3,282,069, granted Nov. l, 1966, both of which patents have been assigned to The Bendix Corporation:

An object of the invention is to provide monitoring and testing means which depends on full time operation of auxiliary equipment for maintaining proper iiight attitude.

Another object of the invention is to provide in a fail operative control system of `an aircraft novel means for effecting automatic detection and elimination of system faults.

Another object of the invention is to provide in such a control system novel means for detection of logic failures in both in-line and off-line devices.

Another object of the invention is to provide novel automatic testing means to assure complete operational performance of an aircraft control system.

Another object of the invention is to provide an aircraft control system fail-operative for single failures.

Another object of the invention is to provide in an aircraft control system novel means whereby multiple dissimilar failures have no effect on system operation except to maintain single failure indication.

Another object of the invention is to provide in such a control system failure indicator means whereby a power supply failure effects the same indication as any other single element failure.

Another object of the invention is to provide in such a control system failure indicator means whereby monitor failures result in fail-safe operation.

Another object of the invention is to provide a novel monitoring and testing system and techniques which insure that (1) prior to take-off, the control equipment of an aircraft is fully operational and will give positive control over the aircraft; and (2) that in the event of an in-ight or pre-flight malfunction, the system will be able to detect this malfunction and take proper corrective action.

Another object of the invention is to provide a novel monitoring and testing system to assure that the overall control system of the aircraft is capable of maintaining proper flight attitude and that the logic is fully oper-ational and thereby give the operator of the aircraft a high degree of equipment confidence and assure the maximum probability of a complete, safe mission.

These annd other objects and features of the invention are pointed out in the following description in terms of thekembodiment thereof which is shown in the accompanying drawings. It is to be understood, however, that the 'drawings are for the purpose of illustration only and are not a definition of the limits of the invention. Reference is to be had to the appended claims for this purpose.

In the vdrawings in which corresponding numerals indicate corresponding parts:

FIGURE l is a schematic block diagram of a fail operative control system embodying the monitoring and testing system of the present invention.

FIGURE 2 is a schematic wiring diagram of the rate gyro signal portion of the system of FIGURE 1.

FIGURE 2A is a schematic -wiring diagram of the servomotor portion of the system of FIGURE 1.

FIGURE 3 is a schematic wiring diagram of the comparator embodied in the system of FIGURES 1, 2, and 2A.

FIGURE 4 is a schematic block diagram showing the yaw damper logic network operative by the comparators shown in the systems of FIGURES 1, 2 and 2A and in detail in FIGURE 3.

FIGURE 5 is a schematic wiring diagram of the module failure indicator embodied in the schematic block wiring diagram of FIGURE 4.

FIGURE 6 is a schematic wiring diagram of the current monitor embodied in the schematic block wiring diagram of FIGURE 4.

FIGURE 7 is a schematic wiring diagram of the level sensor embodied in the schematic block wiring diagram of FIGURE 4.

FIGURE 8 is a schematic wiring diagram of the pushto-test network showing the test relay in operative relation to the comparator control switches of FIGURES 2 and 2A and the fault relay, fault light, check reset light and timing circuit of FIGURES 4 and 9 in operative relation in the circuitry of the push-to-test network.

FIGURE 9 is a schematic wiring diagram of the timing circuit embodied in the push-to-test network of FIGURE 8.

FIGURE l0 is a schematic wiring diagram of a control circuit that may be embodied in the driver units 315A, 317A, 315B, 317B, 400, 402 and 614 of the yaw damper llogic network of FIGURE 4.

FIGURE l1 is a schematic wiring diagram of a control circuit that .may be embodied in the driver unit 420 of the network of FIGURE 4.

FIGURE l2 is a graphical illustration of the sequence of operation of the push-to-test network of FIGURE 8.

FIGURE 13 is a schematic wiring diagram of a network that may be embodied in the yaw rate washout and filter 43A, 43B and 43C of the system of FIGURES 1 and 2.

Referring now to the drawings of FIGURES 1, 2 and 2A, there is indicated a triplicated servo system in which the corresponding elements of each servo mechanism system have been indicated by like numerals to which there have been applied the suiiix A, B and C to distinguish between the respective elements of the rs't and second operating servo mechanism system A and B .and the third model servo system C.

In the triplicated servo system, there are provided three sensors such as single axis rate gyroscopes A, 10B and 10C arranged, as shown in FIGURE 2, to operatively position rotor windings 12A, .12B and 12C, respectively, of synchros 14A, 14B and 14C. The rotor windings 12A, 12B and 12C are energized through electrical conductors 16A, 16B and 16C from suitable sources of constant frequency alternating current 18A, 18B and 18C. The rotor windings 12A, 12B and 12C are inductively coupled to stator windings 20A, 20B and 20C, respectively, of the synchros 14A, 14B and 14C so as to apply through output conductors 22A, 22B and 22C alternating current signals to inputs of suitable type amplifiers in the yaw rate washout and filter units 43A, 43B and 43C, shown by FIGURE 13, as hereinafter explained, and which signals correspond to the angular position of the single axis rate gyroscopes 10A, 10B and 10C, respectively. f-

The gyroscopes 10A, 10B and 10C may be of a type such as disclosed and claimed in a copending U.S. application Ser. No. 327,268, filed Dec. 2, 1963, by Alex Morsewich now U.S. Patent No. 3,240,050, granted Mar. 15, l966, and assigned to The Bendix Corporation. The single axis rate gyroscopes 10A, 10B and 10C maybe 4small rate sensing gyroscopes measuring angular velocity of the aircraft yaw axis in which suitable motors for driving the gyro rotors, not shown, and the signal pick-off synchros 14A, 14B and 14C are powered by suitable alternating current supplied through conductors 16A, 16B and 16C from proper yaw damper power supplies 18A, 18B and 18C.

As described in the U.S. Patent No. 3,240,050, there are embedded in the rotor of each gyroscope 10A, 10B and 10C small permanent magnets and adjacent to the rotor is a winding in which an alternating current voltage proportional to rotor speed is induced when the gyro is running. This Voltage may be applied through output conductors 26A, 26B and 26C and selectively connected, as shown in FIGURE 2, by operator-operative switches 28A, 28B and 28C being positioned to close contacts 30A, 30B and 30C to suitable indicator `means or voltmeters 32A, 32B or 32C to verify the speed of operation of the gyro rotor.

These windings, indicated schematically in FIGURE 8 by the numerals 34A, 34B and 34C, respectively, may be alternately connected by the operator-operative s-witches 28A, 28B and 28C being positioned to close contacts 36A, 36B and 36C and thereby connect the windings 34A, 34B and 34C, respectively, through a switch mechanism 38, including switch elements 38A, 38B and 38C operative by a manual control member 39, as shown schematically in FIGURE 2, and the push-to-test network of FIGURE 8, to selectively connect to opposite terminals of the windings 34A, 34B and 34C the positive and negative terminals of a source of direct current or battery 40. Such selective energization of the windings 34A, 34B and 34C serves to torque the gyroscopes 10A, 10B and 10C in opposite senses, as shown and described in the U.S. Patent No. 3,240,050, and effect the test of the output of the gyroscopes, as hereinafter explained.

Further, as shown and described in the U.S. Patent No. 3,240,050, the rate' gyroscopes 10A, 10B and 10C each includes a magnetic damper cooperating with the gyroscope and rotor' element of the signal pick-off synchros 14A, 14B and 14C to prevent overshoot or excess signal output as a result of vibration.

Thus, by applying a direct current from a source 40, as shown in FIGURE 2, to the' respective torquing windings 34A, 34B and 34C of FIGURE 8, a magnetic field results to apply forceto the permanent magnets in the rotor of the gyroscopes 10A, 10B and 10C, causing the rotor to deflect in the same manner that it would when subjected to a yaw rate. The alternating current electrical yaw rate output signal applied by the synchros 14A, 14B and 14C may then be sensed so as to assure proper 4 operation of the gyroscopes 10A, 10B and 10C and the signal pick-off synchros 14A, 14B and 14C.

Each of the yaw rate signals from the synchros 14A, 14B and 14C is applied through the conductors 22A, 22B and 22C, respectively, to the input of the amplifiers in the filter and washout units 43A, 43B and 43C, respectively. The filter and washout units 43A, 43B and 43C, as shown in FIGURE 13, include a discriminator circuit which converts the alternating -current input signals to direct current signals that can be properly shaped by the filter and a Imodulator to change the shaped direct current back to an alternating current output signal applied across filter output conductors 44A, 44B and 44C, respectively.

As hereinafter explained, the washout and filter units 43A, 43B and 43C take advantage of changes in frequency of the dutch roll characteristics of the aircraft to adjust the yaw damper gain (degrees of rudder commanded per degrees of yaw rate) as required. A higher gain is required when the dutch roll frequency is relatively low (approximately 0.1 cycle per second) as it is for lower air speed conditions, particularly approach and take-olf. Less yaw damper gain is required at the higher frequencies of Dutch roll (approximately 0.2 cycle per second) that are encountered in normal cruise and high speed Hight. The filter is relatively complex in order t0 supply the proper gain for the range of Dutch roll frequencies occurring and is described and explained in greater detail hereinafter.

The filter effectively removes higher frequency signals (5 cycles per second and higher) which might cause undesirable coupling with body bending modes of the aircraft. The washout feature of the circuitry allows the system to synchronize to a constant yaw rate, as during a turn. This is accomplished by implementing the filter so that it has zero gain for steady state Signals.

The outputs 44A, 44B and 44C of all three filter circuits 43A, 43B and 43C, respectively, are connected to the inputs of three intermediate amplitude selective gates 50A, 50B and 50C, each of which may be of a conventional type or of a type such as disclosed and claimed in a copending U .S. application Ser. No. 314,397, filed Oct. 7, 1963, by Harold Moreines, now U.S. Patent No. 3,305,735, granted Feb. 2l, 1967 and assigned to The Bendix Corporation, and in a copending U.S. application Ser. No. 317,970, filed Oct. 22, 1963, by Harold Moreines, and assigned to The Bendix Corporation, assignee of the present invention.

The input network of gates 52A, `52B and 52C of the intermediate amplitude selective gates 50A, 50B and 50C each includes three AND type circuits. Each AND circuit has two inputs which are connected to outputs of the filter circuits 43A, 43B and 43C, as shown by FIG- URE 2 and explained in the U.S. Patent No. 3,305,735.

The AND gate function is to select the lower value signal of the two on an instantaneous basis, for example, a sine wave of one volt peak-to-peak as compared to a sine wave of two volt peak-to-peak has different relative values as to which is most negative of any given time. During the time when the signals are above the referenced center line, the lower peak amplitude signal is more negative than the higher value signal, but -when the signals are below the referenced center line, the higher peakto-peak signal is more negative.

The output network of gates 55A, 55B and 55C of the intermediate amplitude selective gate is by the nature of the diode array an OR gate. The OR gate function is just the opposite to that of the AND gate. The function of the OR gate is to select the higher value signal on an instantaneous basis. Therefore, referring to the referenced FIGURE 2, it may be seen that the intermediate amplitude selective gate selects the intermediate value signal from a three fan-in array.

For any three input signals, the output of all three gates will be the intermediate signal and essentially equal, as

heretofore explained in the copending U.S. application Ser. Nos. 314,397 and 317,970.

As shown in FIGURES 2 and 2A, two of the signal ychains terminate in output conductors 55A and 55B, respectively, leading from the intermediate amplitude selective gates 50A and 50B to respective servo amplifiers 59A and 59B. These amplifiers consist of stages of direct coupled transistor amplification, with quadrature rejection circuitry between stages and a high power push-pull output stage connected through conductors 61A and 61B to control windings 63A and 63B, rsepectively, of conventional type two-phase servo motors 65A and 65B having fixed phase windings l67A and 67B connected through conductors 69A and 69B to the sources of constant frequency alternating current 18A and 18B, respectively.

Directly coupled to the output shafts 71A and 71B of the servo motors 65A and 65B are rate generators 73A and 73B of conventional type. The rate generators 73A and 73B have windings 75A and 75B, respectively, excited by an alternating current from the appropriate yaw damper power supplies 18A and 18B. The generators 73A and 73B have output windings 77A and 77B providing an alternating current signal proportional to motor speed, and of a phase (0 or 180) indicative of direction of rotation of the motors `65A and 65B. The generator output is added to (actually subtracted) the yaw damper signals at the inputs `57A and 57B to the servo amplifiers 59A and 59B and applied through isolation transformers 80A and 80B. The `generator signals provide suitable speed control and damping of the servo motors 65A and 65B.

Each of the fmotors 65A and 65B have the output shafts 71A and 71B thereof drivingly connected through transmission gearings 82A and 82B to shafts 84A and 84B leading to plates 85A and 85B of output clutches 87A and 87B; respectively. The shafts 84A and 84B are further drivingly connected through transmission gearings 90A and 90B to shafts 92A and 92B drivingly connected to rotor windings 94A and 94B of follow-up synchros 96A and 96B. The follow-up synchro rotor windings 94A and 94B are supplied with an alternating current through conductors 97A and 97B leading from the appropriate yaw damper power supplies 18A and 18B.

An alternating current signal induced in stator windings 98A and 98B is applied to output conductors 100A and 100B and added (again actually subtracted) to the yaw damper signal through isolation transformers 102A and 102B at the input to the servo amplifiers 59A and 59B, respectively. Thus, synchros 96A and 96B supply a position follow-up signal for the yaw damper and, when the servo motors 65A and 65B are engaged in a driving control relation with a hydraulic rudder control system 103 through the clutches 87A and 87B, a follow-up signal applied by the synchros 96A and 96B acts with the yaw dam-per signal to control the position of a rudder 104 through the operation of a hydraulic rudder control system 103 which may be of a type such as described in the U.S. Patent No. 3,282,069.

Thus, the yaw damper signal of a given magnitude may cause rotation of the servo motors 65A and 65B until the output from the follow-up synchros 96A and 96B seen at the input of the servo amplifiers 59A and 59B is equal and opposite to the yaw damper signal, at which time the net servo amplifier input will be zero and the servo motors 65A and 65B will stop driving.

Removing the yaw damper input signal at the servo amplifiers 59A and 59B will result in the output signal from the follow-up synchros 96A and 96B being the net input signal to the respective servo amplifiers 59A and 59B, whereupon the servo motors 65A and 65B will be driven in a sense to adjust the rotor windings 94A and 94B to null the output of the synchros. The follow-up synchros 96A and 96B also act as a pre-engaged synchronizer since any noise or nulls in the system will cause the servo motors 65A and 65B to rotate until the rotor windings 94A and 94B of the follow-up synchros 96A and 96B are driven to a position at which the outputs of the synchros cancel the input signals to the servo amplifiers 59A and 59B, causing rotation of the servo motors 65A and 65B to cease.

The clutches 87A and 87B in the yaw damper servos are electromagnetic clutches including clutch plates A and 85B driven by the shafts 84A and 84B and clutch plates 105A and 105B drivingly connected to the operative control shafts 107A and 107B of the rudder control system 103. The clutch plates 85A and 105A and the clutch plates 85B and 105B are spring loaded to the disengaged condition by suitable diaphragm type springs, not shown, and the respective clutch plates may be biased into engaging relation upon energization of servo control solenoids 110A and 110B of the respective clutches 87A and 87B. The energization of the yaw damper servo clutch control solenoids 110A and 110B are controlled by suitable solid state switching, as shown in FIGURE 4. The clutch faces of the respective plates 85A and 105A and 85B and 105B are toothed to prevent any slippage when engaged.

The control shafts 107A and 107B are each operably connected in the hydraulic rudder control system by a preloaded override spring device, not shown, and which may be of a type described and claimed in the U.S. Patent No. 3,282,069.

Also, as shown diagrammatically in FIGURE 2A and explained in U.S Patent No. 3,379,951, the shafts 84A and 84B driven by the servo gear trains 82A and 82B, respectively, include calibrated friction brakes 112A and 112B, assuring that a nominal torque is required to rotate the servo. This braking means 112A and 112B cooperates in the detection of passive servo malfunctions, as heretofore explained in the aforenoted U.S. Patent No. 3,379,951.

Furthermore, as shown in FIGURES 2 and 2A, a third signal chain from the output conductors 57C leading from the intermediate amplitude selective gate 50C leads to a servo simulator which is, in effect, an electromechanical module whose output has the same nonlinear dynamic characteristics and gain as the servo follow-up signals and in which corresponding parts to those heretofore described with reference to the previously described first two signal chains have been indicated by corresponding numerals to which there has been afiixed corresponding numerals bearing the suffix C.

As hereinafter explained, the output of the servo simulator C is used only for comparison and fault identification.

COMPARATORS As shown in FIGURES 2 and 2A, six comparators of identical structure, shown schematically by circuit diagram in FIGURE 3, are provided in this system. Three of the comparators indicated by the numerals 115(1A), 115(2A) and 115(3A) cross compare the outputs from the gyro filters 43A, 43B and 43C, while three other output comparators 115(1B), 115(2B) and 115(3B) cross compare the servo follow-up signals at the output of the synchros 96A, 96B and 96C. Any disagreement between compared signals results in an alarm being effected by a comparator, as hereinafter explained. The comparators may be of identical structure, as shown by the wiring diagram of FIGURE 3, and the circuit for the yaw rate washout and lters 43A, 43B and 43C may be of the structure shown in FIGURE 13, operatively connected with the several comparators 115, as hereinafter explained.

YAW DAMPER SERVO OPERATION The yaw damper servo operating shafts 107A and 107B are connected through the preload spring devices in series with the pilots inputs, as explained in the aforenoted U.S. Patent No. 3,379,951, and, therefore, do not move the rudder pedals. The servo mounts are an integral part of the rudder hydraulic power package 103, a mechanical schematic of which is shown in U.S. Patent No. 3,379,951.

As explained therein, the rudder hydraulic power package 103 is completely dual, with each dual portion being operable by a yaw damper servo, and the arrangement is such that in actual operation the yaw damper servo operated shafts 107A and 107B may be adjusted so as to reduce the amount of rudder activity required of the pilot so that he may superimpose manual commands on the yaw damper movements at any time, in which case the rudder position may be a sum (or difference) of pilot commands and yaw damper commands.

The normal mode of operation of the yaw damper servos is with both servos 65A and 65B engaged through the clutches 87A and 87B in operative relation with the hydraulic rudder control system 103 and at which time the preload of both of the preload spring devices, described and claimed in the aforementioned U.S. Patent No. 3,282,069, allows torque transmission to operate the system. In the event of a failure of one servo, disengagement of the failed servo will be effected by means of the system logic, shown schematically in FIGURE 4 and hereinafter explained. When the failed servo is disengaged, the friction brake in it is also removed from the system. The torque required to command the rudder position is then less, and there is assured the continued operation by the other yaw damper servo of the hydraulic control system and rudder with no degradation of performance.

DETAILED COMPARATOR OPERATION The three gyro lter comparators 115(1A), 115(2A) and 115(3A) and the three follow-up synchro output comparators 115(1B), 115(2B) and 115(3B), each of which may be of a type such as shown in FIGURE 3, and arranged to sense a predetermined voltage difference and provide an output which is a logical 1 or 0, depending upon the difference of the signal inputs. Once any comparator is alarmed, it is locked in the alarm mode until manually reset. n

A schematic wiring diagram of the comparator circuit is shown in FIGURE 3 in which an alternating current signal at the output conductors 44B from the filter 43B and applied at a conductor 120 will be coupled to a base 122 of an NPN type transistor 125 through a capacitor 127 and the divided resistors 129 and 131, with the resistor 131 being connected to a common ground through a conductor 130. The transistor 125 has an emitter 132 and a collector 133. The collector 133 is connected through a resistor 134 and a conductor 135 to a positive terminal of a source of direct current or battery 136 having a negative terminal connected to ground by a conductor 137.

The arrangement is such that the current conducted by the transistor 125 will vary in direct proportion to the input signal applied across the input conductor 120 and a grounded input conductor 121. This will cause a voltage at the output of the emitter 132 to increase as the llnput signal increases. The output is then at a point 139 1ntermediate a pair of resistors 141 and 143 connecting the emitter 132 of the transistor 125 to an emitter 145 of a second NPN 'type transistor 147 having a collector 149 connected through a resistor 150 to the conductor 135 and thereby to the positive terminal of the battery 136i. A base 151 of the transistor 147 is coupled through a capacitor 153 and the divided resistors 155 and 157 to a second input line 160 and the grounded input line 121 vwhich is connected to the resistor 157 through a conductor 158.

A pair of output conductors 44A from a second lter 43A applies an alternating current signal across the grounded input conductor 121 and the input conductor 160. Similarly, the current conducted by the ytransistor 147 will vary in direct proportion to the input signal applied across input conductor 160 and the grounded conductor 121, provided the input signal applied through the conductor 120 vto the transistor 125 does not vary. An increase then in the input signal to thc transistor 147 will cause the voltage at the output of the emitter of the transistor 147 and taken at point 139 to increase as the input signal voltage applied across the input conductor and grounded conductor 121 is increased.

However, in the aforenoted arrangement it will be seen that as the current conducted by transistor 125 increases, the current conducted by an NPN type transistor 162 also increases. The transistor 162 has a collector 164 connected by a conductor 165 to the point 139, a base 167 and an emitter 169 connected through a resistor 171 to a conductor 173 leading through a resistor 175 to the negative terminal of a source of direct current or battery 177 having a positive terminal connected to ground by a conductor 179. The base 167 of the transistor 162 is connected through a conductor 176 and resistor 178 to the grounded conductor 121 and thereby to the grounded positive terminal of the battery 177 through the grounded conductor 179.

An increase then in the current conducted by transistor 162 causes an increase in the voltage drop across the resistor 171, and a consequent decrease in the voltage drop across the base 167 and emitter 169 of transistor 162 which is eiected through a resistor 180 serially connecting the base 167 to an anode of a diode 181 having a cathode element connected to the conductor 173 leading from the resistor 171 and emitter 169 of the transistor 162. This consequent decrease in the voltage drop in the base to'emitter voltage of transistor 162 with the increase in the current conducted by the transistor 162 may be likened to an increase in the impedance from point 139 to the conductor 173 which would in turn result in a change in the effective voltage at point 139. The voltage changes at point 139 effect a corresponding change in the base 151 to emitter 145 relationship of the transistor 147 (under a no signal change at input line 160) and, therefore, a change in the voltage at a point 183 between resistor 150 and collector 149 and applied through an output conductor 184.

The voltage variations at point 183 resulting from the effects of the alternating current input signals are coupled to the base 185 of an NPN -type transistor 187 through conductor 184, a capacitor 189 and a conductor 190. The base 185 is connected to conductor 190 and thereby to a resistor 191 and through the resistor 191 to the grounded conductor 121.

If equal alternating current signals are applied through input conductors 120 and 160, the voltage variations at point 139 due to variations in input voltage at the base 122 of transistor 125 applied through conductor 120 will be the same as the voltage input variations at the base 151 of transistor 147 due to the equal alternating current signal applied at input line 160 and there will be no voltage variation at point 183. However, upon a change in the balanced relationship of the input voltage signals applied at conductors 120 and 160, there will result a voltage at point 183 which is proportional to the difference between the alternating current signals applied at the input lines 120 and 160. Thus, the greater the difference between the voltage signal at one of the input conductors 120 or 160 relative to the other, the greater the output signal voltage at point 183.

The transistor 187 includes a collector 193 connected by a resistor 195 to the conductor 135 leading from the positive terminal of battery 136 and an emitter 197 serially connected by resistors 199 and 200 to the conductor 173 leading through resistor 175 to the negative terminal of the battery 177 and thereby to the battery 136 through grounded conductors 179 and 137.

A diode 201 has an anode element connected to the grounded conductor 121 and the cathode element connected to a point 202 intermediate resistors 199 and 200. With no signal inputs at the conductors 120 and 160, the transistor 187 remains in the nonconductive state and the collector voltage at a point 203 intermediate the collector 193 and resistor 195 is essentially equal to the posi- 9 tive voltage applied by battery 136, causing a positive voltage to be maintained at the base 205 of an -NPN type transistor 207 through the divided resistors 209 and 211 leading from the point 203 to the grounded conductor 121, with the base 205 connected to a point 212 intermediate the divided resistors 209 and 211.

The transistor 207 includes a collector element 215 connected through a resistor 216 to the positive conductor 135 and an emitter element 217 connected by a conductor 218 to a point 219 intermediate the emitter 197 of the transistor 187 and the resistor element 199. The application of the positive voltage to the base 205 of the transistor 207 then renders the transistor 207 conductive from the collector 215 to the emitter 217, whereupon the voltage at a point 210 intermediate the collector 215 and the resistor 216 is relatively low so as to maintain the voltage at the base '220 of a transistor 222 sufficiently low so that the transistor 222 is nonconductive. The transistor 222 includes a collector element 224 connected through a resistor 225 and conductor 226 to a positive terminal of a source of direct current or battery 228 having a negative terminal connected through a conductor 230 to ground. The transistor 222 has an emitter element 232 connected through a conductor 234 to the grounded conductor 121. The maintaining of the voltage at the base 220 of the transistor 222 low so that transistor 222 is nonconductive so long as the alternating current input signals applied to the conductors 120- and 160- do not exceed a predetermined critical differential causes the output applied at a point 234 intermediate the collector and resistor 225 under such relatively balanced input signal conditions to be maintained at a relatively high value.

The low voltage at the point 210 is applied through a diode 255 having a cathode element connected to the point 210 and an anode element connected through a resistor 267 to a cathode element of a second diode 279 which in turn has an anode element connected to a cathode element of a third diode 263 which in turn has an anode element in turn connected through conductor 265 to the base of the transistor 222 so as to apply the negative going voltage at point 210 to the base 220 of the transistor 222 to maintain the transistor 222 under such conditions nonconductive.

It should be noted, however, that a conductor 236 further leads from the output point 203 of the transistor 187 to an anode element of a diode 238 having a cathode element connected ,by a conductor 240 to the point 234 at the collector output of the transistor 222. Further, the line 226 leading from the positive terminal of the battery 229 is connected through a conductor 240 to an anode element of a diode 242 having a cathode element connected by a conductor 245 to a cathode element of a second diode 247 having an anode element connected through a resistor 249 to the conductor 135 leading from the positive terminal of the battery 136. Also, a resistor 251 is connected at one end to the conductor 245 and at the opposite end is connected through a conductor 253 to a point 254 intermediate the anode element of the diode 255 and the resistor element 267 leading to the cathode element of the diode 269.

Furthermore, leading from the conductor 253 is a resistor element 257 connected to an anode element of a diode 259 having a cathode element connected to a conductor 261 leading to a point 262 eintermediate the anode element of the diode 269 and the cathode element of a diode 263 having an anode element connected by a conductor 265 to the base 220 of the transistor 222. Also, a resistor element 267 leads from the cathode element of the diode 269 to the anode element of the diode 255 which is in turn connected through the cathode element thereof to the negative going output point 210 of the transistor 207. Further, connected between the conductor 261 and the grounded conductor 121 is a capacitor 271, and leading between the conductor 265 and the grounded conductor 121 is a resistor 273. An output conductor 275 leads from 10 the output point 234 of the collector 224 of transistor 222.

Thus, when the base voltage at the transistor 222 is kept low so that the transistor 222 is nonconductive, it will be seen that the output across the conductor 275 and the grounded conductor 121 will be high and capable of supplying current from the source of electrical energy or battery 228 through the conductor 275 in a logic l state.

When the `input signals applied at the lines and are sufficiently dierent as to cause a large enough positive pulse on the base of the -transistor 187, the transistor 187 then conducts heavily, lowering the potential at point 203 and at the base 205 of the transistor 207, whereupon the transistor 207 now cuts off, raising the voltage at point 210 which then acts to back bias the diode 255 so that current heretofore diverted therethrough from the voltage dividing resistors 251 and 257 is applied to in turn back bias the diode 269 and effect through the diode 259 a back bias on the diode 263. Such back bias on the diode 263 acts to increase the effective voltage at the base 220 of the transistor 222, causing the transistor 222 to conduct and the output at the point 234 and applied through conductor 275 to go to a lower level or logic 0 state.

Thus, when the transistor 207 cuts oif, causing an increase in the voltage at point 210, the transistor 222 is rendered conductive, lowering the potential at point 234 so that while transistor 222 is conducting, the diode 233 having the cathode thereof connected through conductor 240 to the low potential point 234 and the anode thereof connected through conductor 236 to the point 203 serves to maintain the point 203 and, therefore, the base 205 of transistor 207 at a low potential, effectively latching the transistor 207 in a nonconductive state regardless of the voltage at the base of the transistor 187.

The circuit may be unlatched by applying a negative bias to the base 220 of the transistor 222, causing it to cease conduction and return the output 275 to a high positive voltage output or logic 1 state.

In the actual operation of the system, the base 220 of the transistor 222 is grounded by the closure of a switch in the line 261 which connects the line 261 to ground as a function of the yaw rate washout and filter network 43, as hereinafter explained. The logic output applied through the output conductor 275 from each comparator is operatively connected to appropriate solid state logic modules, as shown in FIGURE 4.

YAW DAMPER LOGIC NETWORK The output conductors 275(1A), 275(2A) and 275 (3A) leading from the comparators 115 (1A), 115 (2A) and 115 (3A) are shown in FIGURE 4 as leading to suitable OR, NAND and NOR gates of conventional type, while the output conductors 275(1B), 275 (2B) and 275(3B) similarly lead from the comparators 115(1B), 115(2B) and 115(3B), respectively, to such gates, as hereinafter explained in detail.

Referring now to the drawings of FIGURES 4, 5, 6 and 7, it may be noted that under normal circumstances, with the alternating current signals at input conductors 120 and 160 being in a substantially balanced condition, the outputs at the conductors 275 of all of the comparators 115(1A), 115(2A) and 115(3A), 115(1B), 115(2B) and 115(3B) are at a logic l state (voltage present) and it follows that the outputs of the six OR gate circuits 300A, 300B, 300C, 300D, 300B and 300F applied at the output lines 305, 307, 308, 309, 310 and 311 under such normal circumstances are also at a (high voltage present) logic 1 state.

i Under normal conditions, there appears a logic l state on the inputs to all six OR gates 300A-300F. Therefore, the OR gate output is also at a logic l state. To translate a failure or logic 0 state on the OR gate output, it requires that all the inputs go to a logic O state. Any logic 1 state appearing on the input of an OR gate independ- 1 1 ent of the number of logic states on that gate will translate a logic 1 state on the output.

As shown in FIGURE 4, the output conductors 305, 308 and 310 from the OR gates 300A, 300C and 300B are connected to the inputs of drivers 315A and 317A which may be of a type shown in FIGURE 10, each having three AND type inputs. The driver 315A has output conductors 318A and 319A, while the driver 317A has output conductors 321A and 323A. The output lconductors 319A and 321A of the drivers 315 and 317 are serially connected and the arrangement is such that a logic l state (voltage present) must be present on all inputs to each driver to result in a voltage output or logic 1 state condition.

Similarly, the output conductors 307, 309 and 311 of the OR gates 300B, 300D and 300F, respectively, are connected to the inputs of drivers 315B and 317B which also may be of the type shown in FIGURE l0, each of the drivers 315B and 317B having three AND type inputs. Further, the driver 315B has output conductors 318B and 319B, while the driver 317B has output conductors 321B and 323B, with the output conductors 319B and 321B being serially connected. The arrangement is such that a logic 1 state must be present on all inputs to each of the drivers 315B and 317B to result in a voltage or logic 1 state output condition.

Thus, the drivers 315A and 317A are connected in series, as are the drivers 315B and 317B, and the OR gates 300A-300F are duplicated to assure that no single logic failure could render the automatic disconnect systern inoperative and allow an active system failure to command rudder movement.

The drivers 315A and 317A control the supply of energizing current to operate the number one yaw damper servo clutch control solenoid 110A upon an operatoroperative yaw damper engaged switch 330A being positioned so as to close switch contact 332A connected to a conductor 333A leading from the output conductor 323A and arranged, as shown in FIGURES 4, 6 and 8, to connect an energizing current from a source of electrical energy or battery 341A through the serially connected drivers 315A and 317A and through the solenoid 110A and the conductor 335A to a current monitor indicated generally by the numeral 337A, which may be of a type shown schematically in FIGURE 6, and through the current monitor circuit, which provides a low resistance, to a grounded conductor 339A. A diode 340A, as shown in FIGURES 4 and 6, has a cathode element connected to the conductor 323A and an anode element connected to ground to provide arc suppression upon the operatoroperative switch 330A being positioned so as to open switch contact 332A.

Similarly, the serially connected drivers 315B and 317B supply current from a source of electrical energy or battery 341B to operate the number two yaw damper servo clutch control solenoid 110B upon an operatoroperatve yaw damper engaged switch 330B being positioned so as to close a switch Contact 332B connected to a conductor 333B leading from the output conductor 323B and arranged to apply an electrical current from the battery 341B through the serially connected drivers 315B and 317B and through the solenoid 110B and conductor 335B to a current monitor 337B, which may be of a type such as shown schematically in FIGURE 6, which provides a low resistance, to a grounded conductor 339B. A diode 340B, as shown in FIGURE 4 and 6, has a cathode element connected to the conductor 323B and an anode element-connected to ground to provide arc suppression upon the operator-operative switch 330B being positioned so as to open switch contact 332B.

The logic and disconnect circuitry for each servo control clutch solenoid 110A and 110B is identical, although powered from separate direct current supplies 341A and 341B, as shown schematically in FIGURE 4.

12 CURRENT MONITOR FIGURE 6 shows the current monitor circuit which supplies logic indicating clutch engagement upon the energizing current being supplied to the solenoid 110. Thus, when the operator-operative switch 330 closes contact 332 and current is applied by battery 341 through the solenoid -control clutch 110, there is a current flow through a resistor 342 to the grounded conductor 339 and the voltage drop across the resistor 342 is such that a positive voltage is applied through a resistor 344 leading from the conductor 335 to a base 343 of an NPN type transistor 345 having a collector element 347 and an emitter element 349.

Moreover, as shown in FIGURE 6, the collector element 347 of the transistor 345 is connected through a conductor 367, resistor 346 and conductor 348 to the positive terminal of battery 40, as shown in FIGURE 8, and :through `resistor 352 and conductor 354 to the positive terminal of a battery 356, as shown in FIGURE 8, upon the operator-operative knob 655 being operated so as to cause switch 650 to open a contact 651 and close a contact 652 and switch 653 to open a contact 654 and close a contact 656. The negative terminals of both battery 40 and battery 356 are connected to a common ground.

The positive terminal of another battery or source of direct current 351, as shown in FIGURE 6, is connected through a conductor 353, a resistor 355, and a conductor 359 to an anode element of a diode 357 having a cathode element connected through a conductor 361 to the collector element 347. The emitter element 349 of the transistor 345 is connected by a conductor 363 tothe conductor 339 leading to a common ground. The battery 351 has its negative terminal connected to a common ground through a conductor 365 so as to thus complete the electrical circuit through the transistor 345.

Thus, when a positive voltage is applied on the base 343 of the transistor 345 upon the solenoid winding being energized, the transistor 345 is caused -to conduct electrical energy heavily between the collector 347 and the emitter 349 with the emitter voltage being essentially at ground. Further, it will be seen `that there is connected to the collector element 347 through the conductors 367 and 368 the cathode elements of diodes 369 and 371 having anode elements connected `to conductors 373 and 375.

Thus, ast the time a positive voltage is applied to the base 343 of the transistor 345 indicative of energization of the servo clutch control solenoid 110, the logic outputs at the conductors 373 and 375 have a low Voltage or logic 0 state due to the resulting conductive state of transistor 345.

Furthermore, the conductive state of the transistor 345 upon the energization of the control solenoid 110 in eifect clamps a base 377 to a second NPN transistor 379 to ground inasmuch as the base 377 of the transistor 379 is connected through a conductor 381 to an anode element of a diode 383 having a cathode element connected by a conductor 385 to the anode element of the diode 357 which in turn has a cathode element connected by the conductor 361 to the collector 347 which is at a low potential in such conductive state of transistor 345. The conductor 381 leading from the base 377 is connected to ground through a resistor 386 leading to the grounded conductor 339.

Further, it will be seen that the second transistor 379 has an emitter element 389 connected t0 the grounded conductor 339 and a collector element 387 connected through a resistor 391 to the positive terminal of a source of direct current 393 which has its negative terminal connected by a conductor 394 to the positive terminal of the source of direct current 351. The elTect then of clamping the base 377 of the transistor 379 to ground by the conductive state of the first mentioned transistor 345 prevents the transistor 379 from conducting and keeps' the logic stale of an output conductor 395 leading from 13 the collector 387 of the transistor 379 at a (voltage present) logic 1 state upon energization of the control solenoid 110.

It will be further noted that, as shown in FIGURE 6, the current monitor 337 includes a conductor 396 which leads from the conductor 385 to a contact 397 which, during inoperation of the system, is closed by a switch element 398 connected to ground and operative by suitable relay means, as hereinafter explained, in the yaw rate washout and filter units 43A and 43B so as to clamp the base 377 of the transistor to ground during such times as the yaw damper engaged control 655 is at the OFF position. However, upon the control 655 being operated to the ON position, the switch element 398 is operatively positioned so as to open the contact and disconnect the conductor 396 from the ground and render current monitor 337 effective for operation;

Thus, in normal operation, upon ydeenergization of the control solenoid 100, as upon a failure thereof, the voltage applied to the base 343 drops to a low or ground potential, whereupon the transistor 345 becomes nonconductive, and the resulting increased positive voltage applied at the collector element 347 through conductors 348 and 354 back biases the controlling diodes 369 and 371 so that the logic of output conductors 373 and 375 changes to a (voltage present) logic l state. Further, such positive voltage applied at the collector 347 acts to back bias the diode 357 which in turn causes the positive voltage applied by the battery 351 to back bias the diode 383, whereupon a resulting Voltage drop across the resistor 386 applies a positive voltage bias to the base 377 of the transistor 379, whereupon the transistor 379 becomes conductive so that the logic state at the output conductor 395 changes to a low voltage or logic state upon such failure or deenergization of the solenoid winding 110.

In effecting the (voltage present) logic l state of the conductors 373 and 375, it should be noted that the same are connected, respectively, to inputs of drivers 400 and 402 which may be of a type shown by FIGURE 10, each having two AND type inputs forward biased, as shown in FIGURE 10, to elfect the (high voltage present) logic 1 state of the conductors 373 and 375 upon the control diodes 369 and 371 being back biased as explained.

The two inputs of the driver 400, as shown in FIG- URE 4, are connected, respectively, to the output conductor 373A from the servo current monitor 337A and to the output conductor 373B from the current monitor 337B, while the driver 402 has one input connected to the output conductor 375A from the current monitor 337A and a second input connected to the output conductor 375B from the current monitor 337B.

Thus, each of the drivers 400 and 402 have one input from each of the servo current monitors for the servo clutch control solenoids 110A and 110B. The operative characteristics of these drivers 400 and 402 are such that both inputs to the driver must be of a logic 1 state to eifect a (high voltage present) logic 1 at the output of the driver to cause illumination of the light 404 connected to the output line 410 from the driver 400 and the light 406 connected to the output conductor 412 of the driver 402.

Thus, as shown in FIGURE 6, the conductors 3173A and 373B and 375A and 375B would be in a (low voltage) logic 0 state when energizing current is applied through the solenoid 110, thereby applying a positive voltage to the base 343 of the transistor 345. In order for both inputs to the drivers 400 and 402 to be in a logic 1 state, energization of both of the control solenoids 110A and 110B for the clutches `85A and 85B must cease to render the transistor 345 of both current monitors nonconductive to apply a back bias to the control diodes 369 and 371 of both monitors 337A and 337B in order for the inoperative indicator lights 404 and 406 to be illuminated and thus indicate such state.

1 4 FAULT LIGHT An additional driver 420 is provided which may be of a type shown in FIGURE ll, having two OR type inputs and a pair of input conductors 422 and 424 so arranged that a (high voltage present) logic l input applied to either conductor 422 or 424 will cause illumination of a fault light 432 by applying electrical energy to an output conductor 426 and through a diode 428 to a iilament of a fault light 432 having an opposite terminal connected to a grounded terminal 434.

Two NAND gates 440 and and 442 of conventional type are provided to control energization of the two input conductors 422 and 424, respectively, for the driver 420. Leading to the inputs of the NAND gate 440 are the output conductors 275'(1A), 275 (2A) and 275 (3A) leading from the respective outputs of the comparators (1A), 115(2A) and 115(3A), While leading to the inputs of the NAND gate 442 are output conductors 275(1B), 275(2B) and 275(3B) as well as output conductors 395A and 395B from the current monitors 337A and 337B as well as an output conductor 445 leading from a module fail indicator 450, the wiring diagram of which is shown schematically in FIGURE 5.

The output conductors from each of the comparators 115(1A), 115(2A) and 115(3A) and 115(1B), 115(2B) and 115(3B), the output conductors 395A and 395B from the respective current monitors 337A and 337B, and the output conductor 445 from the module fail indicator 450 provide inputs to the NAND gate circuits 440 and 442 to control illumination of the fault light 432 and these are normally at a (high voltage present) logic l state. However, should any of the comparators, the current monitors, or the module fail indicator sense an alarm condition, there would be then effected a change in the corresponding output conductor to a (low voltage) 0 logic state, whereupon the output of the associated NAND gate module 440 and 442 will go to a (high voltage present) logic 1 state and cause the driver 420 to turn the fault light 432 on and effect energization of a fault relay winding 448 connected at one end to the conductor 430 and at an opposite end to a grounded conductor 449 to effect a control action, as hereinafter explained. The fault light 432 requires no immediate action on the part of the pilot, but is simply noted for information.

MODULE FAILURE INDICATOR The module failure indicator 450, as shown in FIG- URE 5, includes input conductors 452, 454, 455, 456, 458 and 460 leading from the respective output conductors 305, 308, 310, 307, 309 and 311 of the OR gates 300A, 300C, 300B, 300B, 300D and 300F and which, under normal circumstances as heretofore explained, are at a high voltage present) logic 1 state. These input conductors, as shown in FIGURE 5, lead to the anode element of diodes 462, 464, 466, 468, 470 and 472. respectively. These diodes in turn have a cathode element connected by a conductor 477 to one end of a resistor 479, the opposite end of which is connected by a conductor 481 to a base 483 of an NPN type transistor 485.

The transistor 485 has an emitter element 486 connected by a conductor 487 to a grounded conductor 489, while a resistor 491 is connected between the base 483 and the grounded conductor 489. The transistor 485 has a collector element 493 connected to the cathode element of a diode 495 having an anode element connected through a conductor 497, a resistor 498 and a conductor 499 to a positive terminal of a source 0f electrical energy or battery 500. The negative terminal of the battery 500 is connected by a conductor 501 to the positive terminal of a second source of direct current y503 which has a negative terminal connected to ground through a conductor 505.

Further, the conductor 499 leading from the positive terminal of the battery or source of direct current 500 has suitable resistor elements 507 leading to the respective 15 input conductors '452, 454, 455, 456, 458 and 460. Also leading to the conductor 497 is a cathode element of a diode 509 having an anode element connected by a conductor 511 to a base 513 of a transistor 515. A resistor 517 is connected between the conductor 511 and the grounded conductor 489.

The transistor 515 has an emitter element 521 which is connected through a conductor 523 to the grounded conductor 489 and a collector element 519 connected by a resistor 525 to the positive terminal of the source of direct current or battery 503 having a negative terminal connected to a grounded conductor 505. The output conductor 445 leads from the collector element 519 of the NPN type transistor 515.

The arrangement is such then that so long as the positive voltage or logic 1 state is applied through the input conductors 452-460, the voltage applied to the base 483 of the transistor 485 will render the same conductive and in turn cause a negative charge to be applied to the base 513 of the transistor 515 through the diodes 495 and 509, rendering the transistor 515 nonconductive and a high voltage or logic 1 state condition to be applied at the output conductor 445.

However upon all of the input conductors 452-460 going to a low voltage condition or logic state, a negative charge will then be applied to the base 481 of the transistor 485 which will render the transistor 485 nonconductive and in turn cause the high voltage charge applied through the conductor 497 from the positive terminal of the battery 500 to back bias the diode 509, increasing the positive voltage applied across the resistor 517 to the base 513 of the transistor 515 so that the transistor 515 is then rendered conductive and the voltage applied at the output conductor 445 reduced to a (low voltage condition) logic 0 state.

In such operation, if any one of the conductors 452-460 changes from such low voltage state or remains in a (positive high voltage) logic 1 state, the positive voltage then applied through the corresponding one diode 462-470 would increase the positive voltage applie-d to the base 483 of the transistor 485, whereupon the transistor 515 would once again become nonconductive and the output applied through the conductor 445 increased to a (high voltage present) logic 1 state or non-alarm condition. However, upon the output conductor 445 changing from the nonalarm logic 1 state to the alarm logic 0 state, there would then be effected through the NAND gate 442 and driver 420 an alarm state causing the fault light 432 to be illuminated. The fault light 432 would, of course, be illuminated in the case any of the input conductors 275(1A), 275(2A), 275(3A), 275(1B), 275(2B), 275(3B), 395A, 395B or 445 should go from the (high voltage present) logic 1 state to the (low voltage present) logic 0 state.

LEVEL SENSOR Further, as shown in FIGURE 4, there are provided level sensors indicated generally by the numerals 550A and 550B which may be of the type indicated schematically in FIGURE 7 including an input conductor 552 leading from a point 554 intermediate a pair of resistors 556 and 558 and a point 555 intermediate the serially connected output conductors 319 and 321. The resistor 556 is connected by a conductor 560 to the conductor 318 leading to the positive terminal of a source of electrical energy or battery 341, while the resistor 558 is connected to ground by a conductor 559. The battery 341 has a negative terminal connected to a common ground and is so arranged as to provide a source of electrical energy for the serially connected drivers 315 and 317, heretofore =de scribed.

The input conductor 552 leads to a conductor 565 connected at one end to a cathode element of a diode 567 and at the opposite end to an anode element of a diode 569. The diode 567 in turn has an anode element connected through a conductor 571 and resistor 573 to a base 575 of 16 an NPN type transistor 577. The NPN type transistor 577 has an emitter element 57 8 connected to ground and a collector element 579 connected through a resistor 581 and conductor 582 to a positive terminal of a battery 583 having -a negative terminal connected through a conductor 585 to a common ground.

Also connected between the conductor 582 and the conductor 571 is a resistor element 587 and leading from the base element 575 is a resistor 589 which is in turn connected to a conductor 591 leading to a negative terminal of a battery 593 having its positive terminal connected to a common ground through a conductor 595. There leads from the collector element 579 an output conductor 597 connected to an anode element of a diode 599 having its cathode element connected to a conductor `601, the opposite end of which is connected to the cathode element of a diode element 603. Also leading from the conductor 601 is an output conductor 605.

Further, the input diode 569 has a cathode element connected through a conductor 607 to a cathode element of a Zener diode 609 having a reverse current breakdown characteristic at a critical voltage to effect the operation of the level sensor, as hereinafter explained. The Zener diode y609 has an anode element connected through a co-nductor 611 to a resistor `612 which is in turn connected through a conductor 614 to a base element 616 of an NPN type transistor 618. The transistor 618 has an emitter 620 connected by a conductor `622 to common ground and a collector element 624 connected through a resistor 626 to the conductor 582 leading from the positive terminal of the source of direct current or lbattery 583. Also co-nnected from the conductor 614 leading to the base element `616 is a resistor 628 which is in turn connected to the conductor 622 leading to the common ground.

Further, leading from the collector element 624 of the transistor v61-8 is an output conductor v630 connected to a resistor 632 which is in turn connected through a conductor `634 to a base element 636 of a second NPN type transistor 638 having an emitter element 640 connected to common ground and a collector element y642 connected through a resistor 643 to the conductor 582 leading to the positive terminal of the source of electrical energy or battery 583. Further, leading from the collector 642 of the transistor -638 is an output conductor `645 which is connected to an anode element of the diode 603 and thereby to the output conductors 601 and 605.

The arrangement of the level sensor 550 is such that upon the driver elements 315 and 317 being normally operative and not shorted, the voltage drop across the resistor element 556 and sensed at the input conductor 552 will be equivalent to approximately half that of the voltage of the battery 341 and, in the case of a 28-volt direct current source, las shown, the input voltage at the conductor 552 under such normal operating conditions would be 14 volts.

Such input voltage applied then through the diode 569 would not be suflicient to eiect a reverse current flow through the Zener diode 609 which is so selected as to have a higher reverse current breakdown voltage characteristic than that provided under such normal operating conditions. The Zener diode 609 thus blocks a How of current therethrough from conductor 607 to the conductor 611 and prevents the application of a high voltage therethrough to the base 616 of the transistor 618 under such normal operating conditions. Furthermore, the voltage thus applied through the input conductor 552 to the cathode element of the diode 567 would back bias the diode 567 so as to render the battery 583 elTective to cause a flow of current through the conductor 582, resistors 587, 573 and 589 and conductor 591 to the negative terminal of the battery 593 and in turn apply a positive voltage due to voltage drop across the resistor 589 to the base 575 of the transistor 577, while simultaneously the battery 583 is rendered effective to cause a flow of current through the conductor 582, resistor 626, conductor 630,

17 resistor 632, conductor 634, resistor 635, and conductor 591 to the negative terminal of battery 593 and in turn apply a positive voltage due to voltage drop across the resistor 635 to the base 636 of the transistor 63S and thereby render the respective transistors 577 and 638 conductive to provide a low voltage or negative output at the respective collector output conductors 597 and 645 connected to the anodes of the diodes 599 and 603 so as to effect at the conductor 601 and output conductor 605 a low voltage or logic state under such normal operating condition of the serially connected drivers 315 and 317.

On the other hand, if the driver 315 should have become shorted, the full voltage of the battery 341, in the example given a full 28 direct current voltage, would be applied to the input conductor 552, which voltage would then be applied through the diode 569 to the Zener diode 609. The Zener diode 609 is so selected as to have a reverse current breakdown characteristic at such high voltage so as to permit a reverse flow of current through the Zener diode 609 from the conductor 607 to the conductor 611 and through voltage dividing resistors 612 and 628 to the ground conductor 622. The voltage drop across resistor 628 then causes a positive voltage to be applied to the base 616 of the transistor 618, thereby rendering the transistor 618 conductive, causing in turn a low voltage or negative charge to be applied through the conductor 630, resistor 632 and conductor 634 to the base 636 of the second NPN type transistor 638. The low voltage thus applied to the base 636 of the transistor 638 then renders this second transistor 638 nonconductive, whereupon a high output voltage will be applied through the output conductor 645, diode 603, conductor 601 and output conductor 605, indicating an alarm or (high voltage present) logic 1 state.

Further, if the driver 317 should short, irrespective of whether the driver 315 was operative or not or in a shorted condition, the voltage sensed at the input conductor 552 would be zero or ground potential since the conductor 552 would be connected directly to ground through the shorted driver 317. In such condition, the zero or ground potential voltage applied at the input conductor 552 would then cause a flow of current from the base 575 ofthe transistor 577 through resistor 573, diode 567 and conductors 565 and 552 to ground. This in turn would apply a low voltage of ground potential to the base 575 of the transistor 577 to render the transistor 577 nonconductive and a high output voltage at the output conductor 597 which would be applied through the diode 599 to the output line 605 to provide a positive output indicative of an alarm or logic 1 output condition.

The output conductors 605A and 605B lead from the level sensors 550A and 550B to inputs of a NOR gate 610 of a conventional type and having other inputs to which lead output conductors 395A and 395B leading from the current monitors 337A and 337B as well as inputs to which lead output conductors 275 (1A), 275 (2A) and 275 (3A) from the respective comparators 115(1A), 115 (2A) and 115(3A); inputs to which lead output conductors 275(1B), 275 (12B) and 275 (3B) from the respective comparators 115(1B), 115(2B) and 115(3B) as Well as an input to which leads output conductor 445 from the module failure indicator 450. An output conductor 612 leads from the NOR gate 610 to an input of a driver 614 of a type such as shown diagrammatically in FIG- URE 10.

The NOR gate 610 is effective upon a high positive voltage indicative of a logic 1 state being applied through any one of the aforenoted output conductors to the input of the NOR gate 610 to apply a low voltage to an output conductor 612 leading to an input of the driver circuit 614 having an output conductor 616 connected through a diode 618 to one terminal of a filament 620 of a monitor test lamp 622 having an opposite terminal connected through a conductor 624 to ground. The driver circuit 614 upon which low voltage input from the NOR gate 610 maintains the filament of the monitor test lamp deenergized.

However, only upon all of the output conductors connected to the input of the NOR gate 610 being at a ground potential or at a logic 0 state is the NOR gate 610 then effective to provide a (high voltage present) logic l state at the output conductor 612 leading to the driver circuit 614. The driver circuit 614 is thereupon effective to provide a (high voltage present) logic 1 state at the output conductor 616 so as to `apply electrical energy through the diode 618 to the filament 620 of the monitor test light and through the grounded conductor 624 so as to energize the filament 620 and illuminate the monitor test light 622.

It will be further noted that while the conductors 605A and `605B leading to the NOR gate 610' from the level sensors 550A and 550B are normally at (low voltage present) logic 0 state, the remainder of the conductors 275, 395 and 445 are normally at (high voltage present) logic 1 state and shift to the (low voltage present) logic 0 state upon a failure, However, as hereinafter explained and shown graphically in FIGURE l2, shortly after initiation of phase 2 of the push-to-test sequence, the comparators (1A), l115(2A), 115(3A), 115(1B), 115(2B) and 115(3B) each have one of the compared inputs thereof shorted by the selectively operable switches -650(1A), 650(2A), 650(1B) and 650(2B), whereupon the conductors 275, 395 and 445 shi-ft to the (low voltage present) logic 0 state which, upon the conductors 605A and 605B normally continuing at the (low voltage present) logic 0 state, then cause the NOR gate 610 to effect the illumination of the monitor test light 622 as indicative of a satisfactory completion of the logic interrogation portion of phase 2.

Furthermore, the shifting to the (low voltage present) logic 0 state of the conductors 275, 395 and 445 at the initiation of phase 2 of the push-to-test sequence causes the NAND gates 440 and 442 to effect energization of the fault relay 448 which, as hereinafter explained, conditions a check reset light 725 for illumination through operation `of a timing circuit 682 upon satisfactory completion of phase 2 -of the push-to-test sequence, as hereinafter explained and shown graphically at FIGURE l2. It is also of significant importance that at the end of phase 2 the monitor test light 622 remains illuminated. Since at this time all command signals have returned to null, and, therefore, no error signals are present, the comparators must remain in the alarm mode. The fact that the monitor test light 622 remains illuminated is a positive indication that all comparators have indeed been locked in the failure mode.

DETAILED PRE-FLIGHT TEST CIRCUITRY A pre-flight test circuitry is implemented as shown in FIGURE 8 in which the positive terminal of the source of direct current energy or electrical power 40` is selectively connected upon a switch arm 650 under control of a manually operable control member 655 selectively closing a contact 652, whereupon the test may be initiated upon a second switch member 657 closing a contact 659 -when the aircraft is on the ground by the operation of suitable linkage 661 connecting the switch to the landing equipment of the aircraft.

Thus, upon the switch 650 closing the contact 652 and the switch 657 closing the contact 659, the test operation may then be initiated by the operator pushing a test button 663 which is in turn operably connected to suitable switch elements 665, 669, 673 and `677 so as to cause switch element 665 to close a contact `667, switch element 669 to close a contact 671, switch element 673 to close a contact 675, and switch element 677 to close a Contact 679. The switch elements 665, 669, 673 and 677 are normally biased by suitable spring means indicated schematically by numeral 678 to the positions shown and opening the several switch contacts.

However, upon the test 'button `663 being thus operated to cause the switch element 665 to close the contact 667, the positive source of electrical energy from the battery 40 is then applied to a conductor 680 leading to an input to a timing circuit 682, shown in detail in FIGURE 9 and explained in detail hereinafter.

Moreover, upon the switch 665 cl-osing the contact 667, electrical energy from the battery 40 is applied through a conductor 683 to an electromagnetic winding 685 having an opposite terminal connected through a conductor 687 to ground. The electromagnetic winding 685, upon energization, acts upon an electromagnetic core 689 operably connected to the switch elements 665, 669, 673 and 677 so as to overcome the biasing force of spring 678 and hold the switch elements 665, 669, 673 and 677 and the test push button 663` in the actuated position, whereupon the button 663 need not be held manually by the operator during the test.

Furthermore, the test timer circuit 682, shown in FIG- URE 9 and energized by the switch element 665 closing contact 667 upon the actuation of the test button 663 has timer characteristics, as hereinafter explained, that are such as to provide a positive output voltage at output conductor 690 after the input voltage at the line 680 has been continually supplied to the timing circuit 682 for a predetermined time interval controlled by the timing circuit 682.

When either the electrical power applied at the input conductor 680 to the timing circuit 682 is removed from the timer or the output at line 690 interrupted, the output from the timer 682 at conductor 690 ceases immediately and the timer 682 is reset to begin another timing cycle, as hereinafter explained.

Furthermore, after a predetermined interval of time following initial application of electrical power to the input conductor 4680 to the timing circuit 682, the timing circuit applies a positive output voltage t-o the output conductor 690 which is connected to an anode element of a diode 692 having a cathode element connected through a conductor 694 to a switch arm 696 which is biased by a suitable spring indicated schematically by the numeral `697 into the lower position sho-wn in FIGURE 8 closing a switch contact 698.

The contact 698 is connected through a conductor 700 to a winding 702 having an opposite terminal connected to a grounded conductor 704. Thus, the positive output voltage from the timing circuit 682 is effective upon the switch arm 696 closing the contact 698 to energize the test relay winding 702 by a circuit leading from a source of electrical energy or battery 705 having a positive terminal connected to a conductor 707 leading to the timing circuit 682 and a negative terminal connected through a conductor 709 to a common grounded terminal, as hereinafter explained in reference to the timing circuit of FIGURE 9.

Thus, after a predetermined time controlled by the timing circuit 682, the application of power to the input conductor 680 of the timing circuit 682 causes the battery 705, as shown by FIGURES 8 and 9, to supply a positive output voltage to the conductor 690 and energize the test relay winding 702 through the switch arm 696 biased by the spring 697 into a position to close switch contact 698 of the fault relay 448 to complete phase 1 of the push-totest sequence, illustrated graphically by FIGURE 12.

During this phase 1 of the test, the three rate gyroscopes 10A, 10B and 10C are torqued to simulate a steady yaw rate by means of electrical power supplied through a switch element 715 which is mechanically connected with switch elements 650(1A), 650(2A), `650(1B) and '650 (2B) and biased therewith by a suitable spring 716 to the upper position shown in FIGURE 8, so that switch element 715 closes a switch contact 717. The switch element 715 is connected by a conductor 719 to the input conductor 680 leading to the timing circuit 682, while the contact 717 is connected by a conductor 720 to the respective switch arms 669, 673 and 677 which are held in opposition to the spring 678 in a position closing the switch contacts 671, 675 and 679, respectively, under the electromagnetic force effected by the energization of the holding coil 685 upon the closing of the switch contact 667 by the switch arm 665 on the actuation of the operator-operative push button 663.

The switch contacts 671, 675 and 679 are in turn connected through conductors 681, 683 and 685 to a switch mechanism 38, shown schematically by FIGURE 2, and through switch elements 28A, 28B and 28C closing switch contacts 36A, 36B and 36C so as to energize the torquing windings 34A, `34C and 34B, shown schematically in FIGURE 8, of the respective rate gyroscopes 10A, 10B and 10C which, as heretofore explained, may be of the type shown and described in the copending U.S. application Ser. No, 327,268, led Dec. 2, 1963, by Alex Morsewich now U.S. Patent No. 3,240,050, granted Mar. 15, 1966, and assigned to The Bendix Corporation.

This torquing action, however, is terminated upon the test relay 702 being energized by the output from the timing circuit 682 after the predetermined time delay period controlled thereby. However, prior to this output signal being applied by the timing circuit 682 at the output conductor 690, the three signal chains are exercised by the application of the simulated yaw rate, and the yaw rate washout and iilter circuits of 43A, 43B and 43C, shown in FIGURE 2 and in detail by FIGURE 13, as hereinafter explained, serve to wash out the yaw rate command and the servo motors 65A, 65B and 65C effect command rudder movements in accordance with the outputs of the lter circuits 43A, 143B and 43C. This normally is accomplished without any alarms from any of the comparators (1A), 11.5(2A), 115(3A), 115(1B), 115(2B) and 11.5(3B) indicating that the system is completely operational.

If a comparator alarm should occur during the phase 1 of the test, the fault light 432 and the fault relay 448 will be energized. The energization of the fault relay 448 will in turn cause the electromagnetic force of the relay winding 448 to actuate the switch element 696 in opposition to the biasing spring 697 and out of closing relation with the switch contact 698 and into an upper position closing a switch contact 728. Such opening of the switch contact 698 renders the timer 682 ineffective to energize the test relay winding 702. However, the closing of the switch contact 728 by the switch 696 connects to the output line 694 of the timer 682 a check reset light 725 having a filament 726 which will be energized upon the timer 682 applying an output voltage through the conductor 694 on the expiration of the predetermined time delay provided by the timer 682. The illumination of the check reset light 725 will indicate a need to check the operation of the system.

However, upon successful completion of the system performance segment of the test of phase ll, the test relay winding 702 is energized as a function of the timer 682 so as to generate an electromagnetic force which acts upon an electromagnetic core 733 mechanically connected to the switch elements 715, 650(1A), 650(2A), 650(1B) and 650(2B). The energization of the winding 702 then actuates in opposition to the biasing force of spring 716 the switch element 715 from a position closing the switch contact 717 to a position opening the switch contact 717 and closing a switch contact 730 connected through a conductor 732 to the conductor 700 so as to provide a holding circuit for retaining the test relay winding 702 in an energized condition.

The latter action of the switch element 715 in opening the switch Contact 717 and closing the switch contact 730 removes the power from the circuit for energizing the gyro torquing windings 34A, 34B and 34C, allowing the rate gyroscopes 10A, 10B and 10C to return to neutral and locks the test relay winding 702 by the closing of the contact 730 in the energized condition. 

